1. Field of the Invention
This invention involves improvements to communications systems and methods in a wireless communications system.
2. Description of Related Art
The medium access control (MAC) layer of the ISO/OSI reference model, controls the assignment of a shared transmission medium resource to transmitting stations by using an access method such as time division multiplex, frequency division multiplex, code division multiplex, and the like. In collision oriented multiple access schemes, such as Aloha and Ethernet, if a transmitting station gains access to the shared medium while another station is transmitting on the medium, the transmitted data becomes corrupted. The access method provides an orderly way for the stations to back off from their transmission and retry at a later time. In the Aloha access method, a station broadcasts its packet when ready, the sender listens to see if it collides with other packets, and if so, re-transmits after a random interval. In the Slotted Aloha access method, packets are constrained to start at the beginning of a time slot, the sender listens to see if it collides with other packets, and if so, re-transmits after a random interval, in a later time slot. In Carrier Sense Multiple Access/Collision Detect (CSMA/CD) access methods, such as Ethernet, a transmitting station waits until the medium is quiet before starting to transmit and then continues to listen while transmitting. If two stations transmit during the same interval, both stations detect this and continue to transmit for a certain length of time to ensure that all stations on the medium detect the collision. The transmitting stations then wait for a random interval before attempting to transmit again. Details of the Ethernet access method are provided in the book by Hegering and Lapple, entitled "Ethernet, Building a Communications Infrastructure", Addison-Wesley, 1993. In all applications of multiple access methods, design engineers try to estimate the maximum number of stations that will attempt to gain access to the shared medium in an average interval and then provide a sufficient number of time domain channels, frequency domain channels, or code domain channels, for example, to accommodate those stations.
In wireless communications, the medium is defined by a cell region occupied by a base station that serves a number of remote stations. At least some classes of messages between the remote stations and the base station, such as channel access requests or transmission control messages, employ collision oriented multiple access schemes to gain access to the shared medium, in order to conserve the radio spectrum. When a remote station wishes to request a session with the base station, it uses a collision oriented multiple access scheme. In a crowded interval when two or more remote stations attempt to access the base station, if the base station detects that a collision has occurred on the shared access channel, it can respond by broadcasting a negative acknowledgement (NACK) signal. Many times, however, the base station does not detect that a collision has occurred among requesting remote stations. Alternately, if the remote stations detect that a collision has occurred, they can back off and retry at a later time. But, in either case, it is difficult for the base station to quantitatively assess the reduced performance that the remote stations suffer during the interval of high usage.
What is needed is some way for the base station to have accurate information about the reduced performance that the remote stations suffer during an interval of high usage, to enable the base station to adaptively provide additional channels to the remote stations.